Butterfly valves are commonly used in vacuum pressure control systems, such as those employed in semiconductor fabrication systems. A butterfly valve, or “flapper valve,” typically comprises a thin flapper coaxially disposed within a passageway of the valve housing. The flapper is secured to the valve assembly by a rotatable valve shaft extending laterally across the passageway. Rotation of the valve shaft controls the position of the flapper with respect to the valve housing.
Butterfly valves are capable of providing good control performance and sealing near closed positions by a variety of methods. Most commonly, a radially sealing o-ring is implemented in the flapper. In this case, as the valve approaches the closed position, the o-ring is compressed radially. O-rings are made of an elastomer material allowing them to deform slightly when under compression but having enough elasticity to prevent them from permanent deformation when uncompressed. O-rings can enable a positive vacuum seal of a butterfly valve.
However, the use of o-rings as sealing mechanisms, particularly for valves used in vacuum pressure control systems, carries several disadvantages. O-rings experience a high amount of shear force when sealing, and as a result, they degrade quickly. Additionally, specialized gases used during fabrication processes may react with, or otherwise affect, the elastomer material of the o-ring. Some fabrication processes generate high temperatures and/or pressures which may further degrade the elastomer material.
As a result, o-rings must be replaced frequently. Frequent replacement carries its own disadvantages in addition to the inconvenience of frequent replacement. For example, handling and installing them may introduce contaminants, such as skin oils, lint, or plasticizers from plastic gloves, into an otherwise clean system.